TM 9-4120-357-14
5-18. Sight-Glass Liquid Indicator.
a. Access. Obtain access to the sight-glass liquid indicator by removing 31 screws and washers from the top panel
and removing the panel. Unscrew four panel fastener screws from the front access panel, and remove the panel.
b. Discharge the System. Whenever a leak is detected or a refrigeration component must be replaced, you must
discharge all gas from the refrigeration system in accordance with paragraph 5-6.
c. Removal. Remove the sight-glass liquid indicator from the air conditioner as directed in the following procedure:
(1) Connect a cylinder of dry nitrogen to the gage port of the discharge service valve. Open both service valves,
and crack the nitrogen cylinder shutoff valve open to provide a 1-2 CFM (0.5 -1 M3) flow.
(2) Debraze connections to
the sight-glass liquid indicator (4, Figure 5-2).
(3) Remove two screws, nuts and washers from the retaining bracket (5), and remove the bracket and sight-glass
liquid indicator (4).
d. Installation. Install the sight-glass liquid indicator in accordance with the following steps:
(1) Position the indicator inside the air conditioner casing, and install the retaining bracket (5) with two screws,
washers and nuts, finger-tight. Insert tubing ends into ends of sight-glass indicator tubes.
(2) Provide a flow of dry nitrogen through the system, and braze the joints.
(3) Tighten screws and nuts to secure retaining bracket.
CAUTION
Whenever the refrigeration system has been opened to the atmos-
phere, you must install a new drier-strainer (dehydrator) before
With the refrigeration system discharged and a hose attached to the gage port of the suction service valve, connect a
cylinder of oil-pumped dry nitrogen to the gage port of the high-pressure service valve. Open the high-pressure service
valve, and crack open the cylinder shutoff valve to establish a flow of 1-2 CFM (0.5-1 M3) through the system. Purge for
at least 30 minutes to expel all other gases, impurities and water vapor. Turn off both service valves before disconnect-
ing the nitrogen cylinder and the discharge house.
f. Charging the System. Prepare the refrigeration system for charging by attaching a pressure gage to the high-
pressure service valve gage port, and a pressure hose and drier-strainer, loosely, to the suction service valve gage port.
Leave both valves closed. Proceed as follows:
WARNING
Avoid contact with liquid refrigerant or escaping refrigerant gas.
Irreversible tissue damage can result from sudden freezing. Be
especially careful to protect the eyes. Avoid inhaling high con-
centrations of refrigerant gas, and prevent gas coming into direct
contact with flame or hot metal surfaces; lethal phosgene gas can
be formed.
(1) Connect a cylinder of refrigerant, R22, to the pressure hose. Open the cylinder shutoff valve slightly to purge
the hose of air, then tighten the hose connection to the suction service valve gage port.
(2) Open both service valves and the cylinder shutoff valve. Charge the system with refrigerant gas until the gage
on the discharge (high-pressure) service valve registers 70 PSI (5 KG/CM2). Close the suction service valve and the
cylinder shutoff valve.
(3) Transfer the charging line to a
cylinder of
dry nitrogen. Open the cylinder shutoff valve and the suction service
valve, and let nitrogen flow into the refrigeration system until the discharge pressure gage reads 350 PSI (21.4 KG/CM2).
Close the suction and discharge service valves and the cylinder shutoff valve. Disconnect the charging line from suction
service valve.
5-27